The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, it is desired that HDDs be able to store more information in their limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
The further miniaturization of the various components, however, presents its own set of challenges and obstacles. The development of microwave-assisted magnetic recording (MAMR) systems for enhancing the surface density of magnetic recording media has benefited higher density recording. In MAMR, information is recorded as a result of application of a high-frequency magnetic field of a strong microwave band across a nanometer-order region to locally excite the recording medium within this region and reduce the magnetization-reversing magnetic field. In order to achieve an adequate reduction in the magnetization-reversing magnetic field for utilizing the magnetic resonance, a magnetic field of a proportionally higher frequency than the anisotropy magnetic field of the recording medium is used.
Japanese Laid-Open Patent Application No. 2005-025831 discloses a high-frequency oscillator, which in this reference is a spin torque oscillator (STO) of a structure in which, in order to generate a high frequency-assisted magnetic field, a laminated film of a structure that resembles a giant magnetoresistance (GMR) device. STOs are able to generate a minute high-frequency vibrating magnetic field by injecting conduction electrons with spin fluctuations generated by a GMR structure into a magnetic body by way of a non-magnetic body. A technique in which a spin torque-based high-speed rotating high-frequency magnetic field generating layer is arranged adjacent to a main pole of a perpendicular magnetic head to generate microwaves (high-frequency magnetic field) is described in “Microwave Assisted Magnetic Recording” J-G. Zhu, et al., IEEE Trans. Magn., Vol. 44, No. 1, pp. 125 (2008). This reference also discloses that information is recorded on a magnetic recording medium of high magnetic anisotropy. Furthermore, “Medium damping constant and performance characteristics in microwave assisted magnetic recording with circular as field,” Y. Wang, et al., Journal of Applied Physics, Vol. 105, pp. 07B902 (2009), discloses a technique in which the magnetization reversal of a magnetic recording medium is efficiently assisted by the arrangement of an STO between the main pole of the magnetic recording head and the trailing shield rearward of the main pole, along with a change in the rotating direction of the high-frequency magnetic field in response to the polarity of the recording magnetic field.
In MAMR heads that comprise a STO, an electric current must flow to the STO. As is disclosed in “Medium damping constant and performance characteristics in microwave assisted magnetic recording with circular as field,” Y. Wang, et al., Journal of Applied Physics, Vol. 105, pp. 07B902 (2009), when an STO is arranged between the main pole and the trailing shield, the main pole and the trailing shield serve the additional role of electrodes. An inherent problem in terms of the practicality of such a structure pertains to the difficulty associated with positioning the STO and the main pole, which have widths on the order of several 10's of nanometers. Positioning displacement of these layers gives rise to the possibility of disruption to the uniformity of the electric current applied to the STO, and to obstruction of stable oscillation of the STO. Accordingly, while the width of the STO must be less than that of the main pole, there are limits thereto in terms of improving the high-frequency magnetic field intensity.
Therefore, it would be beneficial to have a MAMR system having a high-frequency magnetic field-assisted magnetic recording head that is capable of stably producing a high oscillation frequency and assisted magnetic field intensity, irrespective of variations in the STO width and a relative positional relationship between the STO and the main pole produced during the manufacturing process. In this way, the surface recording density and ease of manufacturing and manufacturing yield would be able to be improved.